1. Field of the Invention
The present invention relates, in general, to a three-dimensional shape measurement apparatus and method using the Moire principle and Stereo vision principle, and more particular, to a three-dimensional shape measurement apparatus and method, which is implemented in order to prevent the error of 2π ambiguity from occurring in a measurement method using the Moire principle, thus more precisely measurement of the shape of a measurement target.
2. Description of the Related Art
Several techniques including an optical triangulation method using a laser structured light, a stereo vision method using two intensity images, the Moire technique, etc. have been developed to measure the three-dimensional (3-D) shapes of objects. Among these methods, the Moire measurement method has widely been used because it offers excellent precision and short time for measuring timely measurement of 3D shape. However, it has an inherent limitation: 2π ambiguity, which occurs when target objects have a depth greater than the pitch of a projected fringe pattern. Therefore, in the prior art, when the phase difference between a location to be measured and a nearby reference location is more than 2π, the problem of the 2π ambiguity is solved by correcting the height value by adding ±2Nπ, where N is an arbitrary natural number. However, the conventional 3-D shape measurement method using the Moire principle still has a problem in that, if two measurement objects are spaced apart from each other by a distance of 2π or more, it is difficult to determine whether the resultant value of measurement is caused by the 2π ambiguity or that it indicates a measurement object having a depth of more than 2π. Consequently, incorrect measurement results may occur. Therefore, in the prior art, much effort was devoted to solving 2π ambiguity using other methods.
Technology disclosed in Korean Patent Laid-Open Publication No. 10-2005-0031328 and entitled “3-D inspection method and apparatus using stereo vision and Moire” involves a scheme in which a light projection unit projects a certain pattern several times, and a target object is measured using two cameras respectively while shifting the phase of the fringe pattern using a actuator. Such technology based on the above scheme can accumulate 3-D shape information every time while shifting the phase of the fringe pattern. The plurality of pieces of 3-D shape information measured in this way can then be compared with each other, and finally the 3-D shape information about the measurement object is obtained. However, this technology is problematic in that, even if the 3-D shape information about the object can be relatively precisely measured while eliminating 2π ambiguity, hardware, such as an actuator for shifting the phase of the fringe pattern, must be provided. In addition, considerable time is required to measure the 3D shape of the object.